1. Field of the Disclosure
The present disclosure relates to a non-contact power transmission apparatus that supplies electrical power to a secondary battery in an electronic apparatus.
2. Description of Related Art
In recent years, a power source has been provided that can charge a secondary battery in a terminal device in a non-contact state in which a terminal of another device, such as a charging device, that supplies power, or the like is not connected to the terminal device.
As a non-contact power transmission method that has hitherto been performed, an electromagnetic induction method is known. This is such that a power transmission coil is arranged in an apparatus on the side in which electrical power is transmitted, and a power receiving coil is arranged on the power-receiving-side terminal device. In this electromagnetic induction method, the power transmission coil of the power-transmission-side apparatus is brought into proximity of the power receiving coil of a power-receiving-side apparatus, both the coils are flux-coupled, and electrical power is supplied in a non-contact manner.
This electromagnetic induction method is a non-contact power transmission technology that has hitherto been known. The transmissible distance is approximately several mm, and electrical power can be transmitted only among devices that are very near. For this reason, currently, the electromagnetic induction method is used in some devices, such as water-proof terminal devices in which it is difficult to expose a charging terminal.
In comparison, in recent years, as a method for efficiently supplying electrical power in a non-contact manner to a terminal device at a long distance to a certain degree, a method called a magnetic-field resonance method has begun to be developed and put into the market. This is such that an LC circuit formed of a coil, a capacitor, and the like is provided in each of a power-transmission-side apparatus and a power-receiving-side apparatus, and magnetic fields are made to resonate between both the circuits, thereby transmitting electrical power in a wireless manner. In order to cause the magnetic fields to resonate between both the circuits, it is necessary to make the frequencies at which the resonance is performed equal to each other.
In the case of the magnetic-field resonance method, transmission at a short distance of approximately several cm to several m becomes possible. Furthermore, if there are a plurality of power-receiving-side apparatuses within the transmissible range, electrical power transmission can be performed simultaneously from one power-transmission-side apparatus to the plurality of power-receiving-side apparatuses.
A technology is described in Japanese Unexamined Patent Application Publication No. 2010-183812 in which, in order to improve the efficiency of non-contact power transmission, a plurality of primary side coils are arranged in one row in a horizontal direction on the power transmission side, and coils which are combined in which the electrical power transmission efficiency is high are selected when electrical power is to be transmitted to a secondary side coil.
As described above, in a case where a plurality of secondary side coils are arranged in one row in a horizontal direction, it is possible to deal with a position displacement of the power-receiving-side apparatus with respect to the direction in which the secondary side coils are arranged. However, in a case where the position is displaced in a direction different from the direction in which the secondary side coils are arranged, it is not possible to increase transmission efficiency even if any of the coils is used. Furthermore, if a large number of secondary side coils are to be arranged, the configuration of the power-transmission-side apparatus becomes complex as the number of coils arranged increases.
In addition, in the case of the magnetic-field resonance method, electrical power can be transmitted from a primary side coil to a plurality of power-receiving-side apparatuses. However, if a large primary side coil is arranged, which can efficiently transmit electrical power to a plurality of power-receiving-side apparatuses at the same time, efficiency is not good much when electrical power is transmitted to only one power-receiving-side apparatus by the one large primary side coil.